In cast molding methods of producing ophthalmic devices, such as ocular inserts and contact lenses, a reaction mixture or polymerizable composition is commonly cured in a device-shaped cavity defined by a first mold member with a device-forming molding surface and a second mold member with a device-forming molding surface, or a female and male mold member, respectively. The mold members are typically produced by injection molding a thermoplastic polymer into mold-shaped cavities. Examples of thermoplastic polymers which can be used to make ophthalmic device molds include non-polar thermoplastic polymers, such as polypropylene, polystyrene, and polyethylene; and polar thermoplastic polymers, such as ethylene-vinyl alcohol copolymers and poly(vinyl alcohol) homopolymers. When cast molding ophthalmic devices, after placing the polymerizable composition in the first mold member, the first and second mold members are placed together or coupled together to form a mold assembly with an ophthalmic device-shaped cavity therebetween. The mold assembly is then cured to polymerize the polymerizable composition, forming the polymeric ophthalmic device in the device-shaped cavity of the mold assembly.
Contact lenses, including silicone hydrogel contact lenses, have been cast molded in molds made of ethylene-vinyl alcohol (EVOH) copolymers, for example SOARLITE™ S available from Nippon Gohsei, Ltd., Osaka, Japan. Molding silicone hydrogel lenses in EVOH molds has been found to result in lenses having ophthalmically acceptably wettable surfaces. Previously, it was necessary to apply a surface treatment such as, for example a plasma treatment, or to include an interpenetrating network of a polymeric wetting agent in silicone hydrogel ophthalmic devices in order for the device surfaces to be ophthalmically acceptably wettable when hydrated. However, EVOH is an expensive material which is essentially insoluble in water. The high cost of EVOH molds can negatively impact production costs. Additionally, it can be difficult to release the polymeric ophthalmic device body from EVOH mold members following curing, which can negatively impact device yields and production costs.
It has also been proposed to use poly(vinyl alcohol) homopolymers (PVOH), including modified forms of PVOH, to form ophthalmic device molds, including contact lens molds. The use of ophthalmic device molds which are water-soluble could be particularly useful and cost-effective, as it could simplify the process of releasing the device from the molds while also reducing the possibility of damaging the device during the release process. However, the use of many forms of PVOH has been found not to be ideal for use as ophthalmic device lens molds. For example, as the traditional melt processing temperature and thermal degradation temperature of unmodified PVOH are almost the same, it is very difficult to use these materials to injection mold ophthalmic device molds. Although PVOH is water-soluble, it can be difficult to achieve complete dissolution of the material, particularly at low water temperatures, and solutions of PVOH typically do not exhibit stable viscosities, as they gel readily and crystallize when subjected to high shear conditions.
While some modified forms of PVOH have been proposed for use as ophthalmic device molds, these modified forms of PVOH still retain some of the undesirable properties of unmodified PVOH, such as, for example, high crystalline content that reduces light transmission through the material, slow dissolution in water at lower temperatures, and, when dissolved, significant portions of the material may remain present as undissolvable solids. Further, as with unmodified PVOH, aqueous solutions of modified PVOH can gel or foam easily, and the materials may produce cloudy aqueous solutions due to precipitation of the PVOH material. Although the prospect of an ophthalmic device mold that could be dissolved in water would be attractive, these undesirable properties make it difficult to use either modified or unmodified forms of PVOH in commercial production of ophthalmic devices, including ocular inserts and contact lenses.
In view of the above, it can be appreciated that a need exists for ophthalmic device molds comprising new types of materials for cast molding ophthalmic devices including silicone hydrogel ophthalmic devices, for new ophthalmic devices cast molded using molds comprising these new types of materials, for packaged ophthalmic devices cast molded using molds comprising these new types of materials, and for associated manufacturing methods which use these new types of materials which can be less expensive and more process-friendly. A need exists particularly for water-soluble materials which can be used to form molds suitable for molding contact lenses.
All publications, including patents, published patent applications, scientific or trade publications and the like, cited in this specification are hereby incorporated herein in their entirety.